The present invention relates to a coupling for selectively transferring torque from a torque input member to a torque output member. In particular, the present invention relates to a programmable coupling having a plurality of operating modes for selectively transferring torque between a clutch housing and a race.
One-way clutches and couplings are widely used in the automotive industry for transferring torque between an input shaft and an output shaft when the input shaft is rotating in one direction relative to the output shaft and for allowing the input shaft to freewheel in the opposite direction. As a result, one-way clutches have been used in torque converters and automatic transmissions to allow an input member to drive an driven member while allowing freewheeling to occur between the input member and the driven member when necessary. Examples of such one-way or overrunning clutches presently in use include sprag clutches and roller-ramp clutches.
The sprag clutch generally comprises an outer race, an inner race, and a plurality of wedge-like elements disposed between the inner and outer race. The geometry of the sprag element is such that it allows the clutch to freewheel in one direction, but becomes wedged between the inner and outer race to lock up the clutch in the opposite direction. The roller-ramp clutch is similar to the sprag clutch but includes a plurality of roller elements in replacement of the sprag elements.
A variant of the conventional roller ramp clutch is taught by Rockwell (U.S. Pat. No. 2,085,606) and includes a plurality of graduated-sized roller elements. Since these devices rely on a wedging action to lock up, the sprag elements, roller elements and races are subjected to extremely high radial stresses during lock up. Further, the sprag and roller elements subject the clutch to vibrations while freewheeling. As a result, such one-way clutches an prone to frequent failure.
Spiral-type one-way clutches have been developed as an improvement over sprag and roller-ramp clutches. State of the art spiral-type one-way clutches, such as that taught by Kerr (EP 0 015 674) comprise an outer member having an inner spiral race, an inner member having an outer spiral race congruent with the inner spiral race, and a plurality of elongate roller bearings disposed between the inner and outer race. The elongate roller bearings reduce the frictional resistance to the differential rotation of the spiral surfaces while providing an even distribution of compression forces on the roller bearings and races. However, as conventional spiral-type one way clutches, and one-way clutches in general, only have a single mode of operation, namely lock up in one direction and freewheeling in the opposite direction, the design of automotive equipment using such clutches is unnecessarily over complicated.
Although Rockwell teaches a two-way roller ramp-type clutch, the graduated-sized roller elements can cause spalling of the roller elements and limit the indexing rate of the clutch. Therefore, it would be desirable to provide a reliable coupling having multiple modes of operation and high indexing rates, but without drastically increasing the cost of the coupling.
It is an object of the present invention to overcome or reduce the problems associated with the prior art one-way clutches by providing a spiral-type coupling having multiple modes of operation.
The spiral-type coupling, according to the invention, comprises a tubular member including a first tubular surface; a resilient tubular slipper coaxial to the tubular member and including a first tubular friction surface, a second tubular surface opposite the first tubular friction surface which, together with the first tubular surface, defines a channel disposed between the tubular member and the slipper; a plurality of roller elements disposed in the channel for allowing limited rotational movement between the tubular member and the slipper; a race including a second tubular friction surface disposed adjacent the first tubular friction surface; and an actuator for selectively engaging the second tubular friction surface with the first tubular friction surface.
The tubular slipper includes a pair of adjacent end walls extending between the first tubular friction surface and the second tubular surface along the length of the slipper for allowing the diameter of the slipper to vary in accordance with the position of the actuator.
The first tubular surface comprises at least one clockwise-oriented spiral surface and at least one counterclockwise-oriented spiral surface. The second tubular surface is substantially congruent with the first tubular surface. Preferably, the spiral surfaces are involute spiral surfaces so that the first tubular surface and the second tubular surface remain parallel to each other as the slipper is rotated relative to the tubular member.
In one embodiment of the invention, the slipper comprises a plurality of slipper segments, and the actuator comprises a single actuator ring which engages the slipper segments for selecting between a first mode in which the race freewheels in both directions relative to the tubular member, and a second mode in which the race is locked in both directions to the tubular member.
In another embodiment of the invention, the slipper comprises a plurality of slipper segments, and the actuator comprises a pair of actuator rings which engage alternate slipper segments for selecting between a first mode in which the race freewheels in both directions relative to the tubular member, a second mode in which the race is locked in both directions to the tubular member, a third mode in which the race freewheels in the clockwise direction but is locked to the tubular member in the counterclockwise direction, and a fourth mode in which the race freewheels in the counterclockwise direction but is locked to the tubular member in the clockwise direction.